Lipoproteins contained in blood are classified into chylomicron, very low density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), low density lipoprotein (LDL) and high density lipoprotein (HDL) depending on the difference in density by ultracentrifugation. These lipoproteins are known to have varying contents of lipids such as triglyceride and cholesterol, and proteins. Each lipoprotein has a different function in vivo.
RLP is an intermediary metabolite of the lipoproteins such as chylomicron and VLDL, having a large content of triglyceride. Although RLP is usually metabolized rapidly and removed from blood, when some metabolic disorders occurred, the RLP remains and accumulates in the blood. The RLP is likely to deposit on the artery wall, and is considered to be one of arteriosclerosis-inducing lipoproteins.
As a method for quantifying cholesterol in RLP, a method is known wherein RLP is separated from serum by using affinity gel containing anti-apo A-I monoclonal antibody and anti-apo B-100 monoclonal antibody, and cholesterol contained in the separated RLP is measured, and a reagent therefor is commercially available.
On the other hand, as a method for quantifying RLP cholesterol without requiring separation operations, a method has been recently reported wherein a sample is treated with a cholesterol esterase, cholesterol oxidase or cholesterol dehydrogenase, and phospholipase (Patent Literature 1). In addition to this, a method using two kinds of surfactants (Patent Literature 2), a method using a cholesterol esterase wherein the ratio of lipoprotein lipase activity and cholesterol esterase activity is from 12 to 7000 (Patent Literature 3) and a method using a surfactant having a benzenesulfonic acid structure or a polyacrylic acid surfactant (Patent Literature 4) have been reported.